The invention relates to a polymeric material based on an aliphatic polyol(allyl carbonate). Polymerizates of aliphatic polyol(allyl carbonates) are generally known, e.g., from C. E. Schildknecht, High Pol., Vol. 18, pp. 306-325 (1973). They find frequent use in optical applications, more particularly lenses, on account of such favourable properties as a relatively high index of refraction, high clarity, satisfactory dye receptivity, and reasonable hardness. However, it is desired that the impart strength of polymers be increased.
It should be noted that the improvement of the impact strength of polymeric materials based on aliphatic polyol(allyl carbonate) was proposed before: in U.S. Pat. No. 4,360,653 aliphatic polyol(allyl carbonate) is copolymerized with urethane acrylates. However, no properties other than impact strength are given for these copolymers. On the basis of p. 316 of the publication by Schildknecht referred to hereinbefore the use of urethane acrylates can be expected to lead to a significant degree of yellowing. Moreover, polyurethane acrylates have the drawback of a complex synthesis--this is in contradistinction to the compounds suitable for use in the invention--and are susceptible to water.
The invention has for its object to increase the impact strength relative to the homopolymerizate of the aliphatic polyol(allyl carbonate) by at least 50% without other properties being detrimentally affected. This object is accomplished by forming a specific interpenetrating network of an aliphatic polyol(allyl carbonate) and an aliphatic or cycloaliphatic epoxy resin.
By the well-known term "interpenetrating polymer network", hereinafter to be abbreviated to IPN, is meant a material containing two networks, at least one of which is formed in the presence of the other. Thus, in J. Chem. Soc., p. 1311 (1960) Miller has described an IPN of styrene and divinyl benzene prepared by a known divinyl benzene-styrene resin being permeated with a divinyl benzene-styrene monomer solution and these monomers subsequently being polymerized. When use is made of monomer mixtures each polymerized differently, an IPN can alternatively be produced by simultaneous polymerization. In the IPN's according to the invention the polyol (allyl carbonate) is polymerized by a radical chain reaction, and the epoxy resin is formed by step polymerization.
In rare cases there may be molecular mixing in an IPN. The final polymeric material will then have one glass transition temperature. Generally, the polymers form separate and dissimilar phases, so that the material will show two glass transitions. This phase separation is the main reason why aromatic epoxy resins should not form part of the IPN's according to the invention. Due to a difference in index of refraction aromatic epoxy resin parts will cause turbidity in a polyol(allyl carbonate). This problem can be overcome by selecting aliphatic or cycloaliphatic epoxy resins.
IPN's according to the invention should not be confused with copolymers of polyol(allyl carbonate) and epoxy group-containing olefin monomers, e.g., glycidyl acrylate. Such copolymers are known from U.S. Pat. No. 4,138,538, which discloses an improved polymerization method in which both the polyol (allyl carbonate) and the epoxy group-containing monomers are polymerized under the influence of irradiation.
The polymeric materials according to the invention can be utilized for the manufacture of a wide range of optical products, such as corrective plano lenses for spectacles, more particularly for protective goggles, lenses in optical instruments, guards, transparent covers for watches, measuring instruments, and the like. Because of their satisfactory dye receptivity the materials also are very suited to be used in the manufacture of tinted optical products, such as sunglasses.